This invention relates generally to the field of digitally controlled printing devices, and in particular to continuous ink jet printers in which a liquid ink stream breaks into droplets, some of which are selectively deflected.
Traditionally, digitally controlled color printing capability is accomplished by one of two technologies. Both require independent ink supplies for each of the colors of ink provided. Ink is fed through channels formed in the printhead. Each channel includes a nozzle from which droplets of ink are selectively extruded and deposited upon a medium. Typically, each technology requires separate ink delivery systems for each ink color used in printing. Ordinarily, the three primary subtractive colors, i.e. cyan, yellow and magenta, are used because these colors can produce, in general, up to several million shades or color combinations.
The first technology, commonly referred to as xe2x80x9cdroplet on demandxe2x80x9d ink jet printing, provides ink droplets for impact upon a recording surface using a pressurization actuator (thermal, piezoelectric, etc.). Selective activation of the actuator causes the formation and ejection of a flying ink droplet that crosses the space between the printhead and the print media and strikes the print media. The formation of printed images is achieved by controlling the individual formation of ink droplets, as is required to create the desired image. Typically, a slight negative pressure within each channel keeps the ink from inadvertently escaping through the nozzle, and also forms a slightly concave meniscus at the nozzle helping to keep the nozzle clean.
Conventional xe2x80x9cdroplet on demandxe2x80x9d ink jet printers utilize a pressurization actuator to produce the ink jet droplet at orifices of a print head. Typically, one of two types of actuators are used including heat actuators and piezoelectric actuators. With heat actuators, a heater, placed at a convenient location, heats the ink causing a quantity of ink to phase change into a gaseous steam bubble that raises the internal ink pressure sufficiently for an ink droplet to be expelled. With piezoelectric actuators, a mechanical stress is applied to a piezoelectric material possessing properties that create an electric field in the material causing an ink droplet to be expelled. Alternatively, an electric field is applied to a piezoelectric material possessing properties that create a mechanical stress in the material causing an ink droplet to be expelled. Some naturally occurring materials possessing these characteristics are quartz and tourmaline. The most commonly produced piezoelectric ceramics are lead zirconate titanate, barium titanate, lead titanate, and lead metaniobate.
For example, in a bubble jet printer, ink in a channel of a printhead is heated creating a bubble which increases internal pressure ejecting an ink droplet out of a nozzle of the printhead. The bubble then collapses as the heating element cools, and the resulting vacuum draws fluid from a reservoir to replace ink that was ejected from the nozzle. Piezoelectric actuators, such as that disclosed in U.S. Pat. No. 5,224,843, issued to vanLintel, on Jul. 6, 1993, have a piezoelectric crystal in an ink fluid channel that flexes when an electric current flows through it forcing an ink droplet out of a nozzle.
U.S. Pat. No. 4,914,522 issued to Duffield et al., on Apr. 3, 1990 discloses a drop on demand ink jet printer that utilizes air pressure to produce a desired color density in a printed image. Ink in a reservoir travels through a conduit and forms a meniscus at an end of an inkjet nozzle. An air nozzle, positioned so that a stream of air flows across the meniscus at the end of the ink nozzle, causes the ink to be extracted from the nozzle and atomized into a fine spray. The stream of air is applied at a constant pressure through a conduit to a control valve. The valve is opened and closed by the action of a piezoelectric actuator. When a voltage is applied to the valve, the valve opens to permit air to flow through the air nozzle. When the voltage is removed, the valve closes and no air flows through the air nozzle. As such, the ink dot size on the image remains constant while the desired color density of the ink dot is varied depending on the pulse width of the air stream.
The dot resolution of the printhead is dependent upon the spacing of the individual nozzles; the closer and smaller the nozzles, the greater the resolution. As this technology requires separate ink delivery systems for each color of ink, typically, at least three ink channels are required to produce the necessary colors. This tends to degrade the overall image resolution because nozzles must be spaced further apart.
The second technology, commonly referred to as xe2x80x9ccontinuous streamxe2x80x9d or xe2x80x9ccontinuousxe2x80x9d ink jet printing, uses a pressurized ink source which produces a continuous stream of ink droplets. Conventional continuous ink jet printers utilize electrostatic charging devices that are placed close to the point where a filament of working fluid breaks into individual ink droplets. The ink droplets are electrically charged and then directed to an appropriate location by deflection electrodes having a large potential difference. When no print is desired, the ink droplets are deflected into an ink capturing mechanism (catcher, interceptor, gutter, etc.) and either recycled or disposed of. When print is desired, the ink droplets are not deflected and allowed to strike a print media. Alternatively, deflected ink droplets may be allowed to strike the print media, while non-deflected ink droplets are collected in the ink capturing mechanism.
Typically, continuous ink jet printing devices are faster than droplet on demand devices and produce higher quality printed images and graphics. However, each color printed requires an individual droplet formation, deflection, and capturing system.
U.S. Pat. No. 1,941,001, issued to Hansell, on Dec. 26, 1933, and U.S. Pat. No. 3,373,437 issued to Sweet et al., on Mar. 12, 1968, each disclose an array of continuous ink jet nozzles wherein ink droplets to be printed are selectively charged and deflected towards the recording medium. This technique is known as binary deflection continuous ink jet.
U.S. Pat. No. 3,416,153, issued to Hertz et al., on Oct. 6, 1963, discloses a method of achieving variable optical density of printed spots in continuous ink jet printing using the electrostatic dispersion of a charged droplet stream to modulate the number of droplets which pass through a small aperture.
U.S. Pat. No. 3,878,519, issued to Eaton, on Apr. 15, 1975, discloses a method and apparatus for synchronizing droplet formation in a liquid stream using electrostatic deflection by a charging tunnel and deflection plates.
U.S. Pat. No. 4,346,387, issued to Hertz, on Aug. 24, 1982, discloses a method and apparatus for controlling the electric charge on droplets formed by the breaking up of a pressurized liquid stream at a droplet formation point located within the electric field having an electric potential gradient. Droplet formation is effected at a point in the field corresponding to the desired predetermined charge to be placed on the droplets at the point of their formation. In addition to charging tunnels, deflection plates are used to actually deflect droplets.
U.S. Pat. No. 4,638,382, issued to Drake et al., on Jan. 20, 1987, discloses a continuous ink jet printhead that utilizes constant thermal pulses to agitate ink streams admitted through a plurality of nozzles in order to break up the ink streams into droplets at a fixed distance from the nozzles. At this point, the droplets are individually charged by a charging electrode and then deflected using deflection plates positioned the droplet path.
As conventional continuous ink jet printers utilize electrostatic charging devices and deflector plates, they require many components and large spatial volumes in which to operate. This results in continuous ink jet printheads and printers that are complicated, have high energy requirements, are difficult to manufacture, and are difficult to control.
U.S. Pat. No. 3,709,432, issued to Robertson, on Jan. 9, 1973, discloses a method and apparatus for stimulating a filament of working fluid causing the working fluid to break up into uniformly spaced ink droplets through the use of transducers. The lengths of the filaments before they break up into ink droplets are regulated by controlling the stimulation energy supplied to the transducers, with high amplitude stimulation resulting in short filaments and low amplitudes resulting in long filaments. A flow of air is generated across the paths of the fluid at a point intermediate to the ends of the long and short filaments. The air flow affects the trajectories of the filaments before they break up into droplets more than it affects the trajectories of the ink droplets themselves. By controlling the lengths of the filaments, the trajectories of the ink droplets can be controlled, or switched from one path to another. As such, some ink droplets may be directed into a catcher while allowing other ink droplets to be applied to a receiving member.
While this method does not rely on electrostatic means to affect the trajectory of droplets it does rely on the precise control of the break off points of the filaments and the placement of the air flow intermediate to these break off points. Such a system is difficult to control and to manufacture. Furthermore, the physical separation or amount of discrimination between the two droplet paths is small further adding to the difficulty of control and manufacture.
U.S. Pat. No. 4,190,844, issued to Taylor, on Feb. 26, 1980, discloses a continuous ink jet printer having a first pneumatic deflector for deflecting non-printed ink droplets to a catcher and a second pneumatic deflector for oscillating printed ink droplets. A printhead supplies a filament of working fluid that breaks into individual ink droplets. The ink droplets are then selectively deflected by a first pneumatic deflector, a second pneumatic deflector, or both. The first pneumatic deflector is an xe2x80x9con/offxe2x80x9d or an xe2x80x9copen/closedxe2x80x9d type having a diaphram that either opens or closes a nozzle depending on one of two distinct electrical signals received from a central control unit. This determines whether the ink droplet is to be printed or non-printed. The second pneumatic deflector is a continuous type having a diaphram that varies the amount a nozzle is open depending on a varying electrical signal received the central control unit. This oscillates printed ink droplets so that characters may be printed one character at a time. If only the first pneumatic deflector is used, characters are created one line at a time, being built up by repeated traverses of the printhead.
While this method does not rely on electrostatic means to affect the trajectory of droplets it does rely on the precise control and timing of the first (xe2x80x9copen/closedxe2x80x9d) pneumatic deflector to create printed and non-printed ink droplets. Such a system is difficult to manufacture and accurately control resulting in at least the ink droplet build up discussed above. Furthermore, the physical separation or amount of discrimination between the two droplet paths is erratic due to the precise timing requirements increasing the difficulty of controlling printed and non-printed ink droplets resulting in poor ink droplet trajectory control.
Additionally, using two pneumatic deflectors complicates construction of the printhead, requires more components, and reduces print speed. The additional components and complicated structure require large spatial volumes between the printhead and the media, increasing the ink droplet trajectory distance. Increasing the distance of the droplet trajectory decreases droplet placement accuracy and affects the print image quality. Print speed is reduced because two air valves must be turned on and off. Again, there is a need to minimize the distance the droplet must travel before striking the print media in order to insure high quality images. There is also a need to maintain and/or improve print speed.
U.S. Pat. No. 6,079,821, issued to Chwalek et al., on Jun. 27, 2000, discloses a continuous ink jet printer that uses actuation of asymmetric heaters to create individual ink droplets from a filament of working fluid and deflect thoses ink droplets. A printhead includes a pressurized ink source and an asymmetric heater operable to form printed ink droplets and non-printed ink droplets. Printed ink droplets flow along a printed ink droplet path ultimately striking a print media, while non-printed ink droplets flow along a non-printed ink droplet path ultimately striking a catcher surface. Non-printed ink droplets are recycled or disposed of through an ink removal channel formed in the catcher.
While the ink jet printer disclosed in Chwalek et al. works extremely well for its intended purpose, using a heater to create and deflect ink droplets increases the energy and power requirements of this device.
It can be seen that there is a need to provide an ink jet printhead and printer of simple construction having simplified control of individual ink droplets; an increased amount of physical separation between printed and non-printed ink droplets; an increased amount of deflection for non-printed ink droplets; and reduced energy and power requirements capable of rendering high quality images on a wide variety of materials using a wide variety of inks.
An object of the present invention is to simplify construction of a continuous ink jet printhead.
Another object of the present invention is to simplify control of individual ink droplets in a continuous ink jet printhead.
Yet another object of the present invention is to increase the amount of physical separation between ink droplets of a printed ink droplet path and ink droplets of a non-printed ink droplet path.
Yet another object of the present invention is to increase the amount of deflection of non-printed ink droplets.
Yet another object of the present invention is to reduce energy and power requirements of a continuous ink jet printer.
Yet another object of the present invention is to improve the capability of a continuous ink jet printhead for rendering images using a large volume of ink.
Yet another object of the present invention is to simplify construction and operation of a continuous ink jet printer suitable for printing with a wide variety of inks including aqueous and non-aqueous solvent inks containing pigments and/or dyes on a wide variety of materials including paper, vinyl, cloth and other large fibrous materials.
According to a feature of the present invention, an apparatus for printing an image includes an ink droplet forming mechanism operable to selectively create a stream of ink droplets having a plurality of volumes. Additionally, a droplet deflector having a gas source is positioned at an angle with respect to the stream of ink droplets and is operable to interact with the stream of ink droplets. The interaction separates ink droplets having one volume from ink droplets having other volumes.
According to another feature of the present invention, the ink droplet producing mechanism has a nozzle and may include a heater positioned proximate the nozzle. The heater is operable to selectively create the stream of ink droplets having the plurality of volumes.
According to another feature of the present invention, the heater is operable to be selectively actuated at a plurality of frequencies thereby creating the stream of ink droplets having the plurality of volumes.
According to another feature of the present invention, an ink jet printer for printing an image includes a printhead having a nozzle operable to selectively create a stream of ink droplets having a plurality of volumes. Additionally, a droplet deflector having a gas source is positioned at an angle with respect to the stream of ink droplets. The droplet deflector is operable to interact with the stream of ink droplets. The interaction separates ink droplets having one volume from ink droplets having other volumes.
According to another feature of the present invention, a heater may be positioned proximate to the nozzle with the heater selectively creating the stream of ink droplets having a plurality of volumes.
According to another feature of the present invention, a controller may be electrically coupled to the heater. The controller may selectively actuate the heater at a plurality of frequencies, thereby creating the stream of ink droplets having a plurality of volumes.
According to another feature of the present invention, an apparatus for printing an image includes a droplet forming mechanism. The droplet forming mechanism is operable in a first state to form droplets having a first volume travelling along a path and in a second state to form droplets having a second volume travelling along said path. A droplet deflector applies force to the droplets travelling along the path. The force is applied in a direction such as to separate droplets having the first volume from droplets having the second volume.
According to another feature of the present invention, the force may be a positive pressure force. The force may also be a negative pressure force. The force may also be applied in a direction substantially perpendicular to the path. The force may also include a gas flow.
According to another feature of the present invention, a method of printing an image on a printing media includes selectively forming a stream of ink droplets having a plurality of volumes; providing a gas source at an angle with respect to the stream of ink droplets; separating ink droplets having one volume in the stream of ink droplets from ink droplets having other volumes in the stream of ink droplets; collecting the ink droplets having one volume; and allowing the ink droplets having another volume to contact a print media.
According to another feature of the present invention, a method of diverging ink droplets includes forming droplets having a first volume travelling along a path; forming droplets having a second volume travelling along the path; and causing at least the droplets having the first volume to diverge from the path.
According to another feature of the present invention, causing at least the droplets having the first volume to diverge from the path may include applying a force to at least the droplets having the first volume. Applying the force may include applying the force along the path.
According to another feature of the present invention, applying the force may include applying the force in a direction such as to separate the droplets having the first volume from droplets having the second volume. Additionally, applying the force may include applying the force in a direction substantially perpendicular to the path.